The present invention relates to a method of increasing oil well productivity, by acting on a zone which is near a well.
It is known that the permeability of the near well zone has a decisive influence on its productivity. This zone is in the most stressed condition as for the specific quantity of extraction product which passes through it, and mechanical compression stresses. One of the very important problems in this field is to increase its permeability and reduce sressed in the near well zone.
Known methods of the use of seam-forming reactants are based on dissolving and removal from the near well zone of a part of rock, for example by treatment of carbonate collectors etc. This is disclosed in U.S. Pat. Nos. 4,733,727, 4,703,803, 4,604,218, British patent 2 167 470, and Soviet Inventor's certificates 1 411 441 and 1 476 111. The common disadvantage of these methods is violation of strength of the structure of a new space, which can lead to fast reduction of oil filtration in the seam, and also impossibility of prevention of swelling of minerals of montmorillonite group clays, for example bentonite clays.
A method of hydraulic fracturing of productive seams for forming horizontal cracks is disclosed in U.S. Pat. No. 3,965,982. In accordance with this method, upper and lower packers are installed in the well against the seam, to form contact with the exposed surface of the seam. In accordance with another method disclosed in U.S. Pat. No. 3,976,138, the permeability of productive seams is increased by introduction into the seam treating liquid of aluminous loosening agent. In accordance with still another method disclosed in U.S. Pat. No. 4,007,792 hydraulic fracturing of productive seams is obtained with the use of viscous solutions of surface-active substances. In this method the pressure in the well is increased to the value, at which the cracks in rock are formed, and the pressure is maintained for 0.5-6 hours. Then the pressure is reduced, and the well is emptied.
A method of multiple fracturing of underground seams is known, in which in order to rupture the seam which is opened by the well the working liquid is pumped through the well into the seam and then particulate loosening material is introduced into the cracks. After this, the working liquid is pumped into the well for a next fracturing of the seam, and the particulate loosening materials is introduced into the new crack, as disclosed in U.S. Pat. No. 3,998,271.
It is also known to loosen the cracks in productive seams by introducing a viscous liquid so that it fills the cracks and is retained in them. Then the introduction of liquid is stopped and the crack is left open till the liquid is hardened and loosens the crack, as disclosed in U.S. Pat. No. 4,029,149. Finally, the productive seams can be ruptured by an acid foam. In this method a gel-like solution which contains surface-active substances and inert gas for forming cracks in the seam are introduced into the seam with a sufficient pressure as disclosed in U.S. Pat. No. 4,044,833.
The above described methods are based on formation of hydraulic connection of the productive seam or group of seams with the well through a low-permeability zone or practically impermeable zone which is near to the well and is characterized by increased concentration of stresses. However, when rock is not excavated and no gap-like cavities are formed, no unloading zone in the near well zone will be formed.
The proposal which is the closest to the present invention is disclosed in the publication "Opening of Seams and productivity increase of well", by V.A. Sidorovskii, in "Nedra" Moscow, 1978, page 111. It includes cyclic treatment of the near well zone with seam-treating reactant which is an acid solution. This method has almost universal action on the near well zone, provides productivity increase of wells, their yield, and straightens the profile of advancement of water pumped into the well to maintain the seam pressure. However, this method has a low efficiency for terigen aluminous seams, in which the process is impeded by swelling and peptization of aluminous particles.